The present invention relates to a brake booster for use in automotive vehicles comprising a low-pressure casing sealingly subdivided into a low-pressure chamber and a working chamber by an axially movable wall, the wall having a rigid diaphragm plate and a flexible diaphragm, a reinforcement tube extending axially through the low-pressure casing having its ends fastened to the two end walls of the low-pressure casing, and a mechanically actuatable control valve to connect the working chamber to the low-pressure chamber or to atmosphere, the control valve housing of the control valve being axially movable in the reinforcement tube is in a force-transmitting connection with an actuating piston of a master cylinder and communicates with radial ribs of the movable wall, the ribs projecting through slots in the reinforcement tube.
When striving for a desired weight reduction of automotive vehicles, it is desirable to keep the weight of the brake booster as light as possible.
The transmission of the forces acting between the master cylinder and the brake booster components fastened to the automotive vehicle via a reinforcement tube extending through the low-pressure casing relieves the forces acting on the low-pressure casing so that the casing may be of a very light-weight construction, for instance, of comparatively thin sheet metal or of plastics.
To the end that the overall length of the brake booster be reduced, the diaphragm plate forming the rigid main portion of the axially movable wall was formed integrally with radial ribs, which project through slots into the reinforcement tube to be there connected to a sleeve, which is, on its part, connected to the control valve housing. Such a construction is disclosed in U.S. copending application of R. Becht-P. Bohm, Ser. No. 142,298, filed Apr. 21, 1980, assigned to the same assignee as the present application.
The brake-boosting force generated by the axially movable wall of the above-cited copending application will be transmitted via the radial ribs onto the control valve housing and from there onto the actuating piston of the master cylinder of the brake unit. Because of the comparatively great bending stress occurring in the radial ribs, the diaphragm plate with the radial ribs formed integrally therewith was made of sheet metal and was, as a result, of comparatively heavy weight.